Polymers of conjugated dienes and/or vinyl aromatic hydrocarbons have been produced by numerous methods. However, anionic polymerization of such dienes in the presence of an anionic polymerization initiator is the most widely used commercial process. The polymerization is carried out in an inert solvent such as hexane, cyclohexane, or toluene and the polymerization initiator is commonly an organo alkali metal compound, especially alkyl lithium compounds. The solvent used is almost always a non-polar hydrocarbon because such solvents are much better solvents for the conjugated diene which usually form the largest part of the block copolymers.
As the polymer is created from the monomers, a solution/slurry/suspension of the polymer forms in the inert hydrocarbon solvent. This solution/slurry/suspension is called the polymer cement. These polymerizations may be carried out at a variety of solids contents and it is reasonably obvious that if the process can be run at high solids content, the manufacturing cost will be decreased because more polymer can be produced in a given amount of time.
Unfortunately, with polymer cements of these block copolymers, one of the most significant rate limiting aspects is the viscosity of the polymer cement. For instance, in order to achieve a reasonable efficiency in the removal of hydrogenation catalyst residue from the polymer cement, the viscosity of the polymer cement must not be more than 1000 cp at 80.degree. C. Some of the desired hydrogenated block copolymers can achieve this viscosity requirement so hydrogenation catalyst residue can be efficiently removed at 20% solids, some at 15% solids, but there are other block copolymers that can only achieve the viscosity requirement in polymer cements at close to 10% solids. The manufacturing cost of such hydrogenated block copolymers is therefore much higher. It can be seen that there would be a significant advantage achieved if a way could be found to utilize the current manufacturing technology but decrease the polymer cement viscosity for enhanced catalyst residue removal at higher solids contents so more polymer can be produced in a given amount of time.
It would be desirable to operate the process at a higher solids content in the cement if the same amount of catalyst removal could be achieved in the same amount of time. More polymer would be produced then in a given amount of time. Alternatively, it would be advantageous to be able to decrease the time it takes to remove the desired amount of catalyst residue while operating at the same solids content. The total throughput time would thus be decreased. Another result which would be highly advantageous would be to operate at the same conditions as are presently used (time, solids content, etc.) and thus remove more of the residual hydrogenation catalyst. The present invention provides a method for achieving these goals.